<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>选择器画盒子</title>
    <style>
        .red {
            width: 100px;
            height: 100px;
            background-color: red;
        }
        .blue{
            width:100px;
            height: 100px;
            /*背景颜色background-color*/
            background-color:blue;
        }
    </style>
</head>
<body>
<div class="red">红色</div>
<div class="blue">蓝色</div>
<div class="red">红色</div>
</body>
</html>